Ultrahigh frequency generating tube



M y 1952 M. J10. STRUTT ETAL 2,597,542

ULTRAHIGH FREQUENCY GENERATING TUBE Filed April 18, 1946 2 SHEETSSHEET lMAXIM/LEAN mzas gl %ff Y AZZEQT mmzzzz y 20, 1952 M. J. o. STRUTT EI'AL2,

ULTRAHIGH FREQUENCY GENERATING TUBE Filed April 18, 1946 2 SHEETSSHEET 2l'l'l 25 7 5 5 as .24 5

mm mm; o r o gz ie z i ir BY mmmmma ATTOERZEZ Patented May 20, 1952UNITED STATE ATENT QFFHCE.

ULTRAHIGH FREQUENCY GENERATING TUBE Maximiliaan Julius Otto Strutt andAldert van der Ziel, Eindhoven, Netherlands, assignors, by mesneassignments, to Hartford National Bank and Trust Company, Hartford,Conn., as trustee Application April 18, 1946, Serial No. 662,968 In theNetherlands December 2, 1940 Section 1, Public Law 690, August 8, 1946Patent expires December 2, 1960 quency oscillation by means of anelectrode sys-, 'tem, the velocity variations being then converted intointensity variations and it being possible to derive an output voltagefrom the beam varied in intensity. Such a device may be used for examplefor generating, modulating or amplifying electric oscillations ofultra-high frequen cies.

In the devices of this kind suggested before the velocity control iseffected by the beam of electrons being passed through a control spacebounded by two electrodes and containing one or more electrodessurrounding the electron path and having a controlling ultrahigh-frequency oscillation supplied to them. The velocity variations ofthe electrons in the beam are then converted into intensity variationsand this is preferably effected by the beam being passed through aso-called drift-space in which the slow electrons are overtaken by themore rapid ones so that successive maxima and minima of the electrondensity are set up. Next, energy may be withdrawn from the beammodulated in intensity, for example by the beam being passed through anenergy abstracting space bounded by two bounding electrodes and havingplaced to the electrodes for controlling the velocity of the electronsin the beam.

However, devices of the kind above-described have the disadvantage thatthe required electron valves are comparatively involved and have a greatlength.

The invention has for its object to provide an ultra-high-frequencydevice by means of which the above-mentioned difficulties are obviated.

The device according to the invention comprises a discharge tube inwhich an electron beam is generated and the Velocity of the electrons iscontrolled by an ultra-high-frequency oscillation by means of anelectrode system, the velocity variations being then converted intointensity variations and provision being made for means by which theelectrons varied in velocity are caused to reverse their direction ofmovement during or after the conversion of the velocity variations intointensity variations so that the electrons pass a second time throughthe 2 control electrode system and induce an oscillation therein.

The reversal is preferably brought about by means of a repellingelectrode placed on that side of the control electrode system which isremote from the electrode system for generating the electron beam.

In one convenient embodiment of the invention the-conversion of velocityvariations into intensity variations is effected by means of a driftspace through which the electrons pass before and after the reversal.

In order that the invention may be clearly understood and readilycarried into effect it will now be described more fully with referenceto the accompanying drawings in which convenient embodiments of theinvention are diagrammatically shown and in which,

Figs. 1 and 2 show devices according to the invention comprising one andtwo control electrodes respectively, the reversal of the direction ofmovement of the electrodes being efiected by cans of a repellingelectrode which also serves for converting velocity variations intointensity variations.

Figs. 3 and 4 illustrate two embodiments of the invention in which thereversal of the electrons and the conversion of velocity modulation intointensity modulation is effected by means of a drift space traversedboth before and after the reversal of the electrons.

Referring to Fig. 1, l designates a tube in which provision is made ofan electrode system for generating an electron beam, said system beingconstituted in succession by a cathode 3 heated indirectly by a filamentto which terminals 2 connect and an accelerating electrode 4 and anelectrode 5 serving to concentrate the electron beam. The cathode 3 andthe electrode 5 are earthed and the accelerating electrode 4 has acomparatively low positive potential relatively to the cathode.

In addition, the tube contains a control electrode system comprising twoplate-shaped bounding electrodes 6 and 8 and in between a cylindricalcontrol electrode 1, all of these elec trodes having an identical andhigh direct-current potential relatively to the cathode.

The control electrode 1 is connected to one terminal of an oscillatorycircuit 9 whose other terminal is connected to the bounding electrodes 6and 8.

On that side of the control electrode 1 which is remote from the cathodeis arranged an electrode it having such a negative potential relativelyto the control electrode that electrons accelerated by thefirst-mentioned electrode cannot reach this electrode and thus' rever'setheir direction of movement in its proximity. The electrode it! istherefore referred to as the repell ing electrode. Similarly, electrode5 functions to reverse the direction of electronsleaving the velocitymodulation electrode system I in the direc tion of the cathode.Accordingly, electrode 5 will hereinafter be referred to asth'e-firstepeg-' 102 second; a-third or more times after a time which electrode sinceit is a first repelling "electrode-with: respect to the cathode andelectrode lo wl'llbe referred to as the second repelling electrode.

It is presumed that the operation oftlia'device shown in Fig. 1 may beexplained as follows? For the present it is assumedthat in the circuit 9oscillations occur whose frequency'corre sponds at least substantiallyto the natural'fi'equency of the circuit. Thus, between the-control?electrode 1' and the bounding electrodes 6 and 8 respectively, there areset up twoelectric. alternating fields by which the velocity oftheselecstrons'received from the cathode and accelerated by the boundingelectrode 6'will be controlledin the space between thebounding'electrodes;

By'a suitable choice of the:mean=velocityat which the electrons enterthe controleelectrode system with relation to the lengthof thecontrolelectrode it can be ensured, as isknown per se. that the electronstraverse the'co'ntrolspace in such a time that they are accelerated orretarded by the said two alternatingi fields in dependence on the timewhen the electrons reachthe control space. Thus, the electron beam, onleaving the control space, exhibits a velocity modulation.

The electrons leaving the control space arrive in the field which is'setup'between the electrode l0 and causes the electrons varied in:velocityto reverse their direction of movement. Electrons accelerated inthecontrol-space by the twc alter nating fields will, however, penetrateinto" the repelling field to a further extent than electrons that areretarded by the two alternating fields. Due to this, the path traversedby the accelerated electrons in the repelling field will be larger thanthe path traversed therein by the retarded electrons and the acceleratedelectrons are therefore for a longer time in the repelling field thanthe retarded ones. This, however, means that in the electron beam thatleaves'the repelling field successive maxima and minima of the electrondensity occur or in other words that the velocity variations of theelectron beam are converted. by the' field at least partly intointensity variations.

According to the invention, the electron beam modulated in intensity andleaving the field traverses the control electrode system a second timebut on this occasion in opposite direction and then reaches; the fieldexisting between the bounding electrode 6 and the electrode whichlatter'electmde functions as a repelling electrode. The direction ofmovement of the electrons is thereby reversed again and the velocityvariations of the beam are similarly converted into intensityvariations. The electrons then traverse the controlelectrode system athird time and again arrive in the field set up by the electrode I0 and.so forth.

As is clear from the above electrons in the device shown in Fig. 1perform an oscillating movement in the axial direction of the controlelectrode 1, as is designated in the figure by dotted lines.

It has been found that the electrons which pass through the centre ofthe control electrode about-equaltoor a whole multiple of the oscilation: period of" the oscillatory circuit 9 connectedto the electrode1, 6 and 8. The length of timez-of oneoscillation thereforeapproximately amounts to' an even whole multiple of theoscillationperiod of the oscillatory circuit.

The oscillation induced in the circuit 9 brings about a velocity controlof the electrons in the eaectmm beam as above described and this enablesthe device described to generate self-maintainingpscillationst Dues:toithe fact that the-electrons that pass through the control; electrodesystem a second, a: third: or more times induce an oscillation in thecircuitS energy is abstracted from the oscillating; electrons of thebeam so that their velocity' becomes. less: than the velocity originallybroughtabout bythe potential difference between the. cathode. and theneighbouring accelerating. electrode; Due to this and also due tothemutual-repulsion of the electrons in the beam the electrons, afterhaving performed one or more oscillations; will impinge on a bounding ora:=control;electrode.-

It. hasbeen found that: it is favourable as regards the-efficiency ofthe device according to the-invention: to takemeasures for increasingthe-average number of oscillations performed by theelectrons: before.impinging on a bounding oncontrol electrode.

For: this purpose use may be made of a magnetic field directed intheaxial direction of the control electrode 1. This field can be set up bymeansof one or more coils or else by means of a permanent magnet andconcentrates the electrons-to form a beam.

A further measure for achieving the said object whichv may be used inconjunction with that just mentioned consists in choosing the period ofan oscillation performed by the electrons so as to be-aminimum.v

It. has been found' that for the purpose of obtaining. optimumefficiency with relation to the length of the control electrode 1 in theaxial direction the mean velocity at which the electrons enter thecontrol electrode system should be chosen in such manner that theelectrons traverse the control electrode in a time which corresponds toor is an uneven whole multiple of half the oscillation period Of theoscillatory circuit 9;

In. order to reduce the duration of one oscillation: of the electrons asfar as possible the mean velocity at which. the electrons enter thecontrol electrode 1 is preferably chosen in such manner that theelectrons traverse the control electrode in a time corresponding to halfthe oscillation period of the circuit 9.

It has been found in addition that for the purpose of obtaining optimumefficiency it is necessary' that the direct voltage applied between thecontrol electrode 1 and the repelling electrode should be chosen in suchmanner with relation to the distance between the repelling electrode andthe neighbouring bounding electrode which is nearer thereto that theinterval of time between the moment when the electrons pass through thesaid bounding electrode in the direction of the neighbouring repellinelectrode and the moment when the same electrons pass through thiselectrode in the reverse direction corresponds to or is an uneven wholemultiple of half the oscillation period of the oscillatory circuit.

The said interval of time is therefore a minimum if it corresponds tohalf the oscillation period of the circuit 9.

It follows from the foregoing that the optimum efficiency will beobtained by means of the device shown in Fig. 1 if the duration of oneoscillation performed by the electrons amounts to double the oscillationperiod of the circuit 9.

Fig. 2 shows a device according to the invention in which incontradistinction to Fig. 1 the control electrode system comprises twocontrol electrodes 1a and lb. The parts corresponding to the deviceshown in Fig. l are designated by similar reference numerals.

The control electrodes 1c and lb are connected respectively to theterminals of an oscillatory circuit i2 comprising two parallelconductors and provided with a central tapping e'arthed forhighfrequency currents. This central tapping and the bounding electrodes6 and 8 which are interconnected by a conductor l3 have supplied to thema high positive direct-current potential relatively to the cathode 3.

The operation of the device shown in Fig. 2 is similar to that describedwith reference to Fig. 1. As before, the mean velocity at which theelectrons enter the control electrode system is preferably chosen insuch manner in relation with the length of the control electrodes in andID that the electrons traverse each of the control electrodes in a timecorresponding to half the oscillation period of the oscillatory circuitl2, Since two control electrodes are used the minimum and, as regardsthe efiiciency of the device, optimum duration of one oscillation of theelectrons is triple the oscillation period of the circuit l2.

The conversion of the velocity variations of the beam into intensityvariations which is brought about by the repelling field may be aided bymaking sure that the path traversed in the repelling field by thefastest electrons is considerably longer than the path traversed thereinby the slowest electrons. This may be ensured by the shape of therepelling electrode l ii being chosen in such manner or, if a repellingelectrode assembly is used, by the latter bein shaped and/or arranged insuch manner that the voltage drop of the repelling field in the partwhere the direction of movement of the electrons is reversed isconsiderably lower than in the remaining part of the repelling field.

For this purpose, in the device shown in Fig. 2 in which the secondrepelling electrode is constituted by a disc-like electrode l0 arrangednormally to the axial direction of the control electrodes and having anegative potential relatively to the cathode, and a second electrode [4is arranged in the proximity and on the side of the electrode Ill facingthe neighbouring bounding electrode. This electrod I4 is cylindrical andsurrounds the electron path and its potential corresponds to the cathodepotential.

As already remarked hereinbefore, the electrons, after giving off partof their energy of movement, eventually impinge on one of the electrodesthat surround the control space. Since, however, the electrons whichimpinge on one of the control electrodes 1a, lb bring about unduedamping of the circuit l2 it is desirable that the electrons shouldimpinge substantially on the bounding electrodes 6 and 8.

For this purpose, in the device shown, in which the control electrode orelectrodes is or are cylindrical, the bounding electrodes 6 and 8 eachof which is constituted by a plane plate, preferably comprise circularopenings the diameter of which is smaller than that of the controlelectrode or electrodes, as shown in the figures.

A feature of the device according to the invention consists in that theoscillations set up in the circuit 9 or l2 can be modulated in amplitudein a very simple manner, viz. by providing the electrode system forgenerating the electron beam with a control electrode by means of whichthe intensity of the electron beam can be controlled by a modulationvoltage. Such a control electrode may be constituted for example, as isknown per se, by a control grid placed intermediate the cathode and theaccelerating electrode. In this case, the modulated oscillations may bederived from the circuit 9 or I2, for example by inductive orcapacitative coupling of a load impedance with the said circuits.

Obviously, in the device according to the invention as described it isalso possible to make use of oscillatory circuits different from those.shown. Thus, for example, it is possible to use oscillatory circuits inwhich the control electrodes constitute not only an essential part ofthe capacity of the oscillatory circuit but also part of the inductanceof the oscillatory circuit. Such is the case, for example, if those endsof the control electrodes 1a and lb in the device shown in Fig. 2 whichare remote from each other are connected respectively to the ends of atubular conductor surrounding the control electrodes concentrically.

Figs. 3 and 4 show two embodiments of the invention in which thereversal of the direction of movement of the electrons is brought aboutby means of a repelling electrode but the conversion of velocityvariations into intensity variations is effected by means of a driftspace which is traversed before and after the reversal.

The device shown in Fig. 3 comprises a discharge tube formed by anexhausted glass tube 1 having a reentrant stem 4| at one end and a stem42 at the other end. The tube comprises means for generating an electronbeam having substantially constant intensity and electron speed. Forthis purpose, use may be made of various means and those shown on thedrawing are to be regarded as an example only, the device for generatingan electron beam comprising a filament 3 surrounded by a cathode 3, acontrol electrode l5 and an accelerating anode l6.

During operation of the device the filament 3' is heated by a currentsupplied from a battery l1 and the accelerating anode I6 is given asuitable positive voltage relatively to the cathode which is suppliedfrom a source of voltage l8. The control electrode I5 is given apreferably variable bias which is positive relatively to the cathode andmay be supplied from the source of voltage l9.

Provision is preferably made of some coils 40 which provide a magneticfield parallel to the beam for the purpose of ensuring a sharpconcentration of the electron beam.

The velocity control of the electrons is effected in a control spacebounded by two tubular bounding electrodes23'and 24 which surround thepath of the electron beam are earthed in the case shown and receive ahigh-positive voltage relatively to the cathode from the source ofvoltage. IBM In the form of construction shown inUFig. 3 the controlelectrode system also comprises two control electrodes 26' and 21 whichare similarly tubular and surround the electron beam. The controlelectrodes are connected respectively tov the terminals of anoscillatory .circuit formed by a Lecher line 28 that can be "adjusted tothe'desired length by an'earthed bridge 29., l A

Ifit is'assumed that in the Lecher system 28 oscillations occur whosefrequency corresponds at least'substantially to the natural frequency of'theLecher systemthe velocity of the electrons in the electron beamgenerated in the tube is so controlled by the alternating voltagesupplied to the electrodes Hand 21 that if the length of the controlelectrodes is properly chosen withrelationto the velocity of theelectrons in the electron beam generated by the electrode system '3, I5,I6, the electron beam, which leaves thecontrol space, contains electronshaving a higher and electrons having a lower velocity than the meanvelocity of the electrons.

The electrons that leave the control space then enter the field-freespace enclosed by thegelectrode'24 and referre'dto hereinafter asdriftspace in which the conversion of the said velocity variations intointensity variations is brought about.

The conversion is brought about due to the fact that the acceleratedelectrons tend to overtake the retarded electrons with the result thatgroups of electrons are formed having a greater electron density thanthe mean density of the beam.

Before this process hascom'pletely come to an end the electrons reachthe end of the electrode 2A, there being placed at this end in the pathof the electrons an electrode 25 which is given a voltage negativerelatively to the cathode supplied from the source of voltage 22.The'electrons that leave the drift space arrive in the field set up bythe potential gradient between the electrons 24 andtheso-called'repelling electrode 25, said field bringing about thereversal of the direction of movement of the electrons so that theelectrons pass "through the drift space and the control electrode systema second time. Thus, the conversion of the velocity variations intointensity variations due to the electrons retarded during the control bythe electrodes 26 and 21 bein overtaken by the accelerated electrons isproceeded with after the reversal of the direction of movement of theelectrons, until complete conversion has occurred. The conversion ispreferably completed when the electrons pass through the controlelectrodes '26 and 21 a second time. On the control electrode systembeing passed through a second time an alternating voltage is induced inthe oscillatory circuit connected to the electrodes 26 and 2! by thegroups of electrons of which the beam now consists.

The mean velocity of the electrons in the beam is preferably chosen withrelation to the length of the electrode 24 in such manner, that thephase of the alternating voltage induced in the Lecher line 28 by theelectrons that pass through the electrodes 26 and 21 a second timecorresponds to the phase of the control voltage supplied to theelectrodes 25 and 21. In this case, the induced alternating voltageitself brings about a velocity control of the electrons in the beamwhich permits of selfmaintaining oscillations being generated by meansof the device described.

Intermediate the control-electrode system and the electrode 25 in theproximity of this electrode 'is arranged an electrode 35 surrounding theelectron beam, This electrode 35 is given a bias suitable forconcentrating the returning electrons with the result that the returningelectrons, which enter the control space a second time, are concentratedto form a beam.

In the device shown in Fig. 3 the electrons that pass through the,control space a second time are collected by the accelerating anode I6.this anode having therefore also the function of collecting electrode.

This'doubl'ejfunction of the accelerating anode Ifi involves thedisadvantage that the voltage of this electrode cannot be adjusted tothe optimum value for'both functions. In addition, difticulties mayarise by reason of the intense heating to which the electrode I6 issubjected by the impact with the electrons which have substantiallygiven oif their energy. In a modification of .terial which isconcentrically arranged around thedevice 3, I5, I 6 for generating theelectron beam and in the case shown is enclosed within the tube I. Thisring is placed in the magnetic concentrating field provided by the coils49 and locally brings about such a deformation of this field that themagnetic lines of force between the electrodes 23311111152113 given thecourse designated by cloted lines32. flhe returning electrons, whichsubstantially follow the magnetic lines of force, consequently findtheir way to the ring 3! which therefore also acts as a collectingelectrode and for this purpose is connected via a conductor, 3| shown indotted lines to a suitable positivevoltage from the source of voltagei8. If thering 30 is arranged outside the tube I a, preferably annularelectrode is placed in the path of the lines of force 32 so as tocollect the electrons.

Fig. 4 shows a further form of construction of a device according to theinvention comprising a drift space in which the electrons are deflectedbefore being collected. For this purpose the glass tube I has twobranches I' and I on one side, each of the branches forming a smallangle with the extension of the remaining part of the tube I. The part Icontains a device for generating an electron beam which corresponds tothe similar device shown in Fig. '3. The branch I" of the containerencloses an electrode 20 for collecting the deflected electrons and anelectrode 2| for collecting or suppressing which serves the secondaryelectrons that may be emitted by the electrode 20 and has therefore thefunction of a screen grid -or -suppressor grid respectively. For thispurpose the electrodes 20 and 21 may be given suitable voltagesfrom thesource of voltage I8. In addition in the form of construction shown thebranch. I contains a'special electrode system which comprises electrodes33, 34, 36 and 31 and is substantially similar to the electrode system23, 24, 26, 21 in the part I of the tube shown in Fig. 4.

The electrodes 36 and 37 are connected to a Lecher line 38 comprising ashort-circuiting bridge 39 and tuned to the same frequency as the line28 or, if desired, to a harmonic thereof.

In addition, the space between the electrodes [6, 33 and 23 preferablycontains a magnetic field whose lines of force are normal to thedirection of movement of both the forward and the backward electrons andwhich may be provided by means not shown, for example a horse-shoemagnet. The intensity of this magnetic field is chosen in such mannerthat after passing through this field the beam which is generated by theelectrode system 3, l5, l6 and forms a certain angle with the directionof the axis of the control electrode system 23, 23, 27, 24 enters theelectrode system 23, 26, 21, 24 in the axial direction. The electronswhich after reversal of their movement of direction emerge from theelectrode 23 are again deflected due to the magnetic field, viz. to-

Wards the side of the branch I of the tube I so that they enter theelectrode system 34, 31, 36, 33 in the axial direction. If the length ofthe electrodes and the mean electron velocity are properly chosen thegroups of electrons, on passing through the electrodes 36, 37 induce inthe circuit connected to these electrodes an alternating voltage of thesame frequency as that of the oscillation induced in the line 28 or aharmonic thereof.

The oscillation induced in the line 38 is preferably fed to a loadcircuit (not shown) so that the electrodes 26 and 21 merely serve forvarying the velocity of the beam, whereas energy is abstracted from thebeam by the electrodes 36 and 31. In addition the mean velocity of theelectron beam in this form of construction is chosen in such manner thatthe conversion of velocity variations into intensity variations due tothe retarded electrons being overtaken by the accelerated electrons hasnot been completed until the electrons reach the electrodes 36 and 37.The advantage of a special output-electrode system 34, 31, 36, 33consists in that in the use of such an electrode system it is possibleto choose the various auxiliary voltages at will and so as to be optimumfor the abtraction of energy from the beam.

What we claim is:

1. A high-frequency electron discharge device of the velocity modulationtype, comprising an evacuated envelope and an electron discharge systemmounted therein and comprising, successively, a cathode for generating abeam of electrons, a first repelling electrode perforated to permit thepassage of the primary electron beam generated by the cathode forreversing the direction of flow of electrons travelling in a directiontoward the cathode, an electron velocity modulating electrode systemthrough which the said electron beam passes, and a repelling electrodesystem capable of producing a field configuration for returningsubstantially all electrons leaving the velocity modulatin electrodesystem in a direction away from the cathode, said repelling electrodesystem comprising a first electrode having a passage for electronstherethrough into the system and a second repelling electrode imperviousto electrons and negatively biased with respect to said first electrodeof said system for returning substantially all electrons to the saidvelocity modulation electrode system.

2. A high-frequency electron discharge device of the velocity modulationtype, comprising an evacuated envelope and an electron discharge systemmounted therein and comprising, successively, a cathode for generating abeam of electrons, a first repelling electrode perforated to permit thepassage of the primary electron beam generated by the cathode forreversing the direction of flow of electrons travellin in a directiontoward the cathode, an electron velocity modulating electrode systemthrough which the said electron beam passes, and a repelling electrodesystem capable of producing a field configuration for returningsubstantially all electrons leaving the velocity modulating electrodesystem in a direction away from the cathode, said repelling electrodesystem comprising a disc-like electrode adapted to repel electrons and ahollow cylindrical electrode interposed between the disc-like electrodeand the velocity modulating electrode system and axially aligned withthe electron beam leaving the said electrode system. MAXIMILIAAN JULIUSOTTO STRUTT. ALDERT VAN DER ZIEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 22,506 Hahn June 27, 19442,190,511 Cage Feb. 13, 1940 2,278,210 Morton Mar. 31, 1942 2,320,860Fremlin June 1, 1943 2,347,797 Posthumus et a1. May 2, 1944

